The present invention refers to a high-speed anti-friction bearing, particularly useful for airplane engines.
Anti-friction bearings for airplanes must, like all other airplane parts, be as light as possible. To accomplish that, they should be of small cross sections. Furthermore, they must be suitable for rotation speeds which are as high as possible. These properties have heretofore been obtained in bearings through making the pitch circles of the bearings relatively small, for instance, at most about 250 mm. In this way, speeds of rotation of about 8000 rpm were obtainable. These very high speeds of rotation are possible primarily because the individual parts of the bearing are manufactured with very high precision. Furthermore, the bearing rings have a relatively thick cross section referred to their pitch circle. As a result, upon both manufacture and installation of the bearing, twisting or undulation of the raceways does not occur. Those would otherwise reduce the maximum speed of rotation. Such bearings are known from Federal Republic of Germany DE OS No. 14 25 094 and British Published Application No. 21 09 481.
For their attachment and lubrication, the bearings have flanges which are integrated with the rings. A stiffening effect was provided by these flanges for the rings. But it was unimportant, in view of the large cross sections of the rings.
In modern airplane power plants, the bearings are to be substantially increased in diameter but are to be kept as small as possible in cross section in order to save weight. Such so-called thin-ring bearings are very difficult to manufacture with the required precision. Upon machining of the rings, (for instance, turning the rings on a lathe, hardening and grinding them) stresses are induced. Despite the attachment of the rings in the bearing housing, the stresses lead to inaccuracies, particularly because the housings themselves do not have any great stiffness, in order to save weight.
It is obvious to increase the rotation speeds of such bearings by forming the parts with higher precision. More precise manufacture of the rings to an economically feasible extent produces an increase in the speed of rotation. But this increase is at most only twice the speed obtainable with ordinary thin-ring bearings of the same size. For the speeds of rotation desired in modern airplane power plants, the speeds heretofore achievable, however, are still more than half too slow. This is confirmed in the journal "Aviation Week & Space Technology" of Apr. 13, 1987, page 74, which states that there is still no suitable large bearing.